The present invention generally relates to an electromechanical clutch. More particularly, but not exclusively, the present invention relates to an electromechanical ball clutch for use in a power driven system such as a motorized tailgate or hatchback door for a vehicle, for example.
In power driven systems, there is a need to provide a manual back-up mode in case there is a battery failure, for example. Such a manual back-up mode should provide an effort similar to a standard manual system. It is necessary to disengage a drive unit during the manual back-up mode and also when a user wishes to operate the system manually. One way of allowing disengagement of the drive unit is to provide an electromagnetic clutch between mechanical elements, for example between a motor and a reduction unit that benefits from a lower torque provided by the electromagnetic clutch.
In existing systems, clutching is done by clamping two metal plates together with a magnetic force produced by an electromagnetic coil. The transmitted torque is dependent on a coil pull force and a clutch diameter; i.e., the larger the required torque, the bigger the electromagnetic clutch needs to be. Therefore, in order to have an electromagnetic clutch that transfers a large torque, packaging and weight of the electromagnetic clutch must be increased, which is inconvenient and costly. To reduce the power demand on the electromagnetic coil, a permanent magnet can be added in the electromagnetic clutch to work in conjunction with an electromagnet. The permanent magnetic field of this magnet will then create a permanent drag in the system. When this system is used in a tailgate, for example, this drag can be used to hold the tailgate in an intermediate position without having to keep the power on to power the electromagnetic coil. However, the drag caused by the permanent magnet is very uncomfortable for a user operating a tailgate manually in the event of a power failure because the presence of drag means that it is very difficult to open and close the tailgate.
The present invention has been devised with the foregoing in mind.